Water-cooled electrical apparatus

ABSTRACT

An objective is to prevent excessive temperature decrease of cooling water and to reduce energy loss by a heater. 
     A water-cooled electrical apparatus includes an electrical device  2  placed indoors, a pump  3  for circulating cooling water for cooling the electrical device, a cooler  5,  placed outdoors, for cooling the cooling water, a heater  6  for heating the cooling water, and a main pipe  4  forming a closed loop so that the cooling water circulates through the electrical device, the pump, the cooler, and the heater. 
     The water-cooled electrical apparatus further includes a bypass pipe  11  bypassing between bifurcations  9  and  10,  provided at inlet and outlet sides of the cooler, for flow-dividing the cooling water, and at least one of a first flow amount control valve  7  provided along the main pipe between the bifurcations, and a second flow amount control valve  12  provided along the bypass pipe.

TECHNICAL FIELD

The present invention relates to a water-cooled electrical apparatus cooled by cooling water.

BACKGROUND ART

A conventional water-cooled electrical apparatus has been configured in such a way that an electrical device (such as an inverter) to be cooled, a pump for circulating cooling water cooling the electrical device, and a cooling device for cooling the cooling water heated by heat generated from the electrical device are connected through a pipe to form a closed loop (for example, Patent Document 1).

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Laid-Open Patent Publication H09-199648 (pages 2-3, FIGS. 1-2)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the above described conventional water-cooled electrical apparatus, because, in many cases, the cooling device is placed outdoors, and the apparatus is configured in such a way that the entire amount of the cooling water circulates through this cooling device, when the outdoor temperature decreases, excessive temperature decrease of the cooling water has occasionally occurred. In this case, the difference between the water temperature of the circulating cooling water and the indoor room temperature increases, and due to the temperature of indoor air being decreased to that of the cooling water, the water vapor is saturated to cause dew condensation on the surface of the electrical device whereby a problem for securing insulating ability has occasionally occurred. In order to prevent such dew condensation, the cooling water can be heated by providing a heater at a portion of the closed loop of the cooling water circuit; however, when the cooling water is heated to a level where the dew condensation does not occur, because the temperature decrease of the cooling water is large, a problem has occurred that large energy loss occurs in the heater.

An objective of the present invention, which is made to solve the above described problem, is to prevent the excessive temperature decrease of the cooling water and to reduce the energy loss in the heater.

Means for Solving the Problem

A water-cooled electrical apparatus according to the present invention includes an electrical device placed indoors, a pump for circulating cooling water for cooling the electrical device, a cooler, placed outdoors, for cooling the cooling water, a heater for heating the cooling water, and a main pipe forming a closed loop so that the cooling water circulates through the electrical device, the pump, the cooler, and the heater.

The water-cooled electrical apparatus further includes a bypass pipe bypassing between bifurcations, provided at inlet and outlet sides of the cooler, for flow-dividing the cooling water, and at least one of a first flow amount control valve provided along the main pipe between the bifurcations, and a second flow amount control valve provided along the bypass pipe.

Advantageous Effect of the Invention

According to the water-cooled electrical apparatus of the present invention, the bypass pipe, and at least one of the first flow amount control valve provided along the main pipe between the bifurcations and the second flow amount control valve provided along the bypass pipe are included; thereby, the water temperature can be controlled by varying a mixing ratio between relatively cool cooling water circulating from the main pipe to the electrical device through the cooler and relatively warm cooling water circulating through the bypass pipe to the electrical device. Therefore, because the cooling water can be controlled at higher temperature comparing to the conventional one in which the entire amount of the cooling water circulates through the cooling device, excessive temperature decrease of the cooling water can be prevented and the energy loss by the heater can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a configuration of a water-cooled electrical apparatus according to Embodiment 1 of the present invention;

FIG. 2 is a graph representing a relationship between opening degrees of the first flow amount control valve and the second flow amount control valve in the water-cooled electrical apparatus according to Embodiment 1 of the present invention;

FIG. 3 is a graph representing a relationship between the opening degrees of the flow amount control valves and flow amounts of the cooling water in the water-cooled electrical apparatus according to Embodiment 1 of the present invention;

FIG. 4 is a graph representing a relationship between the opening degree of the flow amount control valve and flow amounts of the cooling water in the water-cooled electrical apparatus according to Embodiment 1 of the present invention;

FIG. 5 is a graph representing a relationship between the opening degree of the flow amount control valve and flow amounts of the cooling water in the water-cooled electrical apparatus according to Embodiment 1 of the present invention;

FIG. 6 is a graph representing an operation mode of the water-cooled electrical apparatus according to Embodiment 1 of the present invention; and

FIG. 7 is a graph representing an operation mode of a water-cooled electrical apparatus according to Embodiment 2 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIG. 1 is a view representing a configuration of a water-cooled electrical apparatus according to Embodiment 1 of the present invention. In this figure, cooling water ejected from an electrical device 2 circulates through a main pipe 4 by a pump 3. In addition to the above, a cooler 5, a heater 6, a first flow amount control valve 7, and a water temperature meter 8 are connected to the main pipe 4, where the main pipe 4 forms a closed circuit in which the cooling water circulates through these units. Bifurcations 9 and 10 for flow-dividing the cooling water are provided at inlet and outlet sides of the cooler 5. A path between both the bifurcations 9 and 10 is bypassed by a bypass pipe 11, where a second flow amount control valve 12 is provided along the bypass pipe 11. Here, numeral 13 schematically represents a boundary between an indoor region in which the electrical device 2 is placed and an outdoor region. In this embodiment, only the cooler 5 and the water temperature meter 8 are placed outdoors, while the other units are placed indoors.

The cooling water heated by the electrical device 2 is pressurized by the pump 3, flows into the cooler 5 through the main pipe 4 in the arrow direction in the figure, and then cooled by the cooler 5 placed outdoors. The cooled cooling water returns to the indoor region again, and then repeats circulation through the main pipe 4. The heater 6 for heating to increase the temperature of the cooling water is provided therein in addition to the electrical device 2, and the water temperature of the cooling water flowing out from the cooler 5 is measured by the water temperature meter 8 provided at an outlet of the cooler 5. Moreover, in the water-cooled electrical apparatus according to this embodiment, a controller 14 is provided to receive a signal relating to the water temperature from the water temperature meter 8 and control the opening degree of the first flow amount control valve 7 or the second flow amount control valve 12 based on the signal.

The cooling-water bypass circuit 11 is provided in this embodiment; accordingly, by controlling the opening degree of the first flow amount control valve 7 provided along the main pipe 4 between both the bifurcations 9 and 10 and the opening degree of the second flow amount control valve 12 provided along the bypass pipe 11, the amounts of the cooling water flowing through the main pipe 4 and the bypass pipe 11 can be controlled. When the first flow amount control valve 7 is opened fully (100%), the second flow amount control valve 12 is closed, while, when the second flow amount control valve 12 is opened fully (100%), the first flow amount control valve 7 is closed, that is, according to graph in FIG. 2, the opening degree of the first flow amount control valve 7 (O_(M)) and that of second flow amount control valve 12 (O_(B)) operate opposite to each other. A relationship between a flow amount of the cooling water flowing through the main pipe 4 (F_(M)) and that through the bypass pipe 11 (F_(B)) in this case is represented, for example, as in FIG. 3.

As described above, when both the first flow amount control valve 7 and the second flow amount control valve 12 are provided in the main pipe 4 and the bypass pipe 11, respectively, the maximum flow amount (F_(MAX)) of the cooling water is flowed into the cooler 5 by setting O_(M)=100% and O_(B)=0%, whereby the maximum performance of the cooling system including the pump 3 and the cooler 5 can be utilized. In contrast, the main pipe 4 is sealed off by setting O_(M)=0% and O_(B)=100% to flow the cooling water only through the bypass pipe 11, whereby the cooler 5 can be maintained as well.

However, in order to obtain an effect according to the present invention, the operation of each opening degree of the flow amount control valves 7 and 12 is not limited to that represented in FIG. 2, and not both the first flow amount control valve 7 and the second flow amount control valve 12 are necessarily provided. For example, even in a case of providing only the first flow amount control valve 7, by controlling the opening degree O_(M) as represented in FIG. 4, the relationship between F_(M) and F_(B) can be controlled. In this case, the main pipe 4 is sealed off by setting O_(M)=0%, whereby the cooler 5 can be maintained. Even in a case of providing only the second flow amount control valve 12 is provided, by controlling the opening degree O_(B) as represented in FIG. 5, the relationship between F_(M) and F_(B) can be controlled. In this case, by setting O_(B)=0%, the cooling water can flow into the cooler 5 at the maximum flow amount (F_(MAX)).

As described above, if at least one of the first flow amount control valve 7 placed along the main pipe 4 between both the bifurcations 9 and 10 and the second flow amount control valve 12 placed along the bypass pipe 11 is provided, the relationship between the flow amount of the cooling water flowing through the main pipe 4 (F_(M)) and that flowing through the bypass pipe 11 (F_(B)) can be controlled. Accordingly, by varying a mixing ratio between relatively cool cooling water circulating from the main pipe 4 to the electrical device 2 through the cooler 5 and relatively warm cooling water circulating from the bypass pipe 11 to the electrical device 2, the temperature of the water can be controlled.

Here, in this embodiment, the configuration in which the cooling water flowing through the main pipe 4 is divided by providing the bypass pipe 11 is adopted; however, by providing only the first flow amount control valve 7 at a position along the main pipe 4 without providing such a flow-dividing circuit, and narrowing the flow amount of the cooling water when the temperature of the cooling water decreases, excessive temperature decrease of the cooling water could also be prevented.

However, there are also many cases where the electrical device 2 is high-voltage equipment; for example, because the front and rear portions of the main pipe 4 where this electrical device 2 is arranged are configured of insulating material (such as poly(tetrafluoroethylene)), the mechanical strength of the portions are weak. If only the first flow amount control valve 7 is provided at a position along the main pipe 4 as described above, the flow amount can indeed be controlled; however, because discharge-pressure control of the pump 3 is generally difficult, if the opening degree of the first flow amount control valve 7 O_(M) is narrowed, water pressure increases. Accordingly, a problem occurs whether the above described weak mechanical-strength portion can resist the increased water pressure.

On the other hand, according to the water-cooled electrical apparatus 1 relevant to this embodiment, because the bypass pipe 11 is provided as the flow-dividing circuit, even in a case of the amount of cooling water flowing through the main pipe 4 being reduced by the first flow amount control valve 7, a certain amount of cooling water can flow through the bypass pipe 11, whereby increase of the water pressure can be relaxed. Therefore, the problem of the water-pressure resistance of the above weak mechanical-strength portion can be resolved.

Next, operation procedures of the water-cooled electrical apparatus 1 according to this embodiment represented in FIG. 1 are explained. First, in a normal operation state in which the cooling-water temperature T_(W) measured by the water temperature meter 8 is relatively high and cooling of the cooling water by the cooler 5 is needed, the controller 14 controls the opening degrees of the first flow amount control valve 7 and the second flow amount control valve 12 so as to operate in an operation region R₁ represented in FIG. 6. That is, in this operation region R₁, the control is performed so as to be the opening degree of the first flow amount control valve 7 O_(M)=100%, and that of the second flow amount control valve 12 O_(B)=0% whereby, by circulating all of the cooling water to the cooler 5, the cooling efficiency is maximized.

In a case in which outdoor temperature decreases and, accompanying the decrease, the cooling-water temperature T_(W) measured by the water temperature meter 8 decreases, if the opening degree of the first flow amount control valve 7 O_(M) is kept at 100%, when cooling water that is overcooled flows into the indoor area, dew condensation might occur depending on indoor humidity at that time. In this case, the controller 14 operates to switch to an operation region R₂ represented in FIG. 6. In this operation region R₂, accompanying the decrease of the cooling-water temperature T_(W), the controller 14 controls to decrease the opening degree of the first flow amount control valve 7 O_(M) from 100% to 0%, and simultaneously increase the opening degree O_(B) from 0% to 100% according to FIG. 2. As described above, by gradually decreasing the amount of the cooling water circulating to the cooler 5, and simultaneously increasing the amount of the relatively warm cooling water flowing through the bypass pipe 11, unnecessary temperature decrease of the cooling water can be prevented without powering on the heater 6.

In a case in which the cooling temperature T_(W) further decreases, the operation mode is set to a state in an operation region R₃ represented in FIG. 6, in which the controller 14 controls the opening degree of the first flow amount control valve 7 O_(M) to keep 0%, and that of the second flow amount control valve 12 O_(B) to keep 100%, so that circulation to the cooler 5 placed outdoors is completely stopped. This means that, because the indoor temperature also decreases accompanying the decrease of the outdoor temperature, heat generation from the electrical device 2 can be balanced with only radiation heat from the main pipe 4 or the bypass pipe 11 placed indoors. Thereby, temperature decrease of the cooling water circulating indoors can be prevented, operating time of the heater 6 placed can be minimized, and energy loss can be reduced more than that of the conventional system.

Moreover, in a case in which the outdoor temperature further decreases, and approaches to temperature T_(F) at which the cooling water freezes, the operation mode is set to a state in an operation region R₄ represented in FIG. 6, in which the controller 14 controls the first flow amount control valve 7 so as to secure the opening degree O_(M) where the cooling water of a minimum flow amount (F_(MIN)) for preventing freezing can flow, and simultaneously controls the second flow amount control valve 12 so as to slightly narrow the opening degree O_(B). Thereby, even when the outdoor temperature decreases, the freezing of the cooling water and breakage of the device caused by the freezing can be prevented.

Boundary water temperatures T₁, T₂, and T₃, respectively between the above described operation regions R₁ and R₂, R₂ and R₃, and R₃ and R₄ may be suitably determined, based on the heat generated by the electrical device 2, the outdoor temperature, the indoor temperature, the indoor humidity, and the following thermal-balance relational equation, setting a goal that the amount of heat generated by the heater is minimized while preventing dew condensation in the indoor device.

Q _(E) +Q _(H) =Q _(C)(T _(W) ,T _(O))+Q _(P1)(T _(W) ,T _(O))+Q _(P2)(T _(W) ,T _(I))

where

-   -   Q_(E) heat generated from the electrical device 2     -   Q_(H) heat generated from the heater 6     -   Q_(C)(T_(W),T_(O)) heat radiating from the cooler 5     -   Q_(P1)(T_(W),T_(O)) heat radiating from the outdoor pipe     -   Q_(P2)(T_(W),T_(I)) heat radiating from the indoor pipe, etc.     -   T_(W) cooling water temperature     -   T_(O) outdoor temperature     -   T_(I) indoor temperature

Additionally, the freezing temperature of the cooling water T_(F) can also be lowered below 0 degree C. (for example, approximately −30 degrees C.) by using conventional antifreeze liquid (ethylene glycol, etc.).

As described above, according to the water-cooled electrical apparatus 1 relevant to this embodiment, because the bypass pipe 11, and at least one of the first flow amount control valve 7 provided along the main pipe 4 between both the bifurcations 9 and 10 and the second flow amount control valve 12 provided along the bypass pipe 11 are included, the water temperature can be controlled by varying the mixing ratio between the relatively cold cooling water circulating from the main pipe 4 to the electrical device 2 through the cooler 5 and the relatively warm cooling water circulating from the bypass pipe 11 to the electrical device 2. Accordingly, because the temperature of the cooling water can be controlled to be higher comparing to that of the conventional system in which the entire amount of the cooling water circulating through the cooling device, excessive temperature decrease of the cooling water can be prevented, and energy loss by the heater can be reduced.

In a case in which, as represented in FIG. 1, both the first flow amount control valve 7 and the second flow amount control valve 12 are provided, in addition to the above effect, the entire amount of the cooling water can flow through the cooler 5; therefore, an effect is also obtained in which the maximum performance of this cooling system can be utilized, and maintenance of the cooler 5 can be performed by sealing off the main pipe 4 at the same time.

Moreover, the water temperature meter 8 for measuring the water temperature of the cooling water flowing out from the cooler 5, and the controller 14 that receives a signal related to the water temperature from the water temperature meter 8, and controls, based on the signal, the opening degree of the first flow amount control valve 7 or the second flow amount control valve 12 are provided; therefore, the amount and the temperature of the cooling water flowing through the main pipe 4 and the bypass pipe 11 can be suitably controlled according to the measured temperature of the cooling water, and the energy loss by the heater can be further reduced.

Embodiment 2

In Embodiment 1, the example has been represented in which, when the temperature of the cooling water approaches the temperature T_(F) at which the cooling water freezes, the amount of the cooling water circulating through the cooler 5 is varied stepwise up to F_(MIN) by opening the first flow amount control valve 7 having been closed. This embodiment is characterized in that, instead of such stepwise variation, by gradually increasing the opening degree O_(M) of the first flow amount control valve 7 and decreasing the opening degree O_(B) of the second flow amount control valve 12, the flow amount through the main pipe 4 is slowly varied to F_(MIN).

In Embodiment 1, because the first flow amount control valve 7 is opened stepwise at the time when the temperature of the cooling water decreases to the predetermined level (T₃), increase of the water temperature by heating by the heater 6 cannot catch up to decrease of the water temperature by the cooled water flowing into the room at once, and thereby the electrical device 2 is transiently cooled, as a result, dew condensation might occur. In contrast, in Embodiment 2, because the cooled water is mixed thereinto with taking enough time from a stage before the temperature of the cooling water has decreased to T₃, which can be compensated by increasing of the water temperature by heating by the heater 6, an effect is also obtained that dew condensation does not occur because the water temperature in the room does not decrease so much.

EXPLANATION OF REFERENCES

-   1: Water-cooled electrical apparatus -   2: Electrical device -   3: Pump -   4: Main pipe -   5: Cooler -   6: Heater -   7: First flow amount control valve -   8: Water temperature meter -   9: Bifurcation -   10: Bifurcation -   11: Bypass pipe -   12: Second flow amount control valve -   14: Controller 

1. A water-cooled electrical apparatus comprising: an electrical device placed indoors; a pump for circulating cooling water for cooling the electrical device; a cooler, placed outdoors, for cooling the cooling water; a heater for heating the cooling water; a main pipe forming a closed loop so that the cooling water circulates through the electrical device, the pump, the cooler, and the heater; a bypass pipe bypassing between bifurcations, provided at inlet and outlet sides of the cooler, for flow-dividing the cooling water; and at least one of a first flow amount control valve provided along the main pipe between the bifurcations, and a second flow amount control valve provided along the bypass pipe.
 2. A water-cooled electrical apparatus as recited in claim 1, further comprising: a water temperature meter for measuring water temperature of the cooling water flowing out from the cooler; and a controller that receives a signal related to the water temperature from the water temperature meter, and controls, based on the signal, an opening degree of the first flow amount control valve or the second flow amount control valve.
 3. A water-cooled electrical apparatus as recited in claim 2, wherein the controller controls in such a way that the higher the water temperature is, the larger the opening degree of the first flow amount control valve is set, or the smaller the opening degree of the second flow amount control valve is set.
 4. A water-cooled electrical apparatus as recited in claim 1, wherein both the first flow amount control valve and the second flow amount control valve are provided. 